There is conventionally known a variable compression ratio mechanism for an internal combustion engine, which uses a double-link piston-crank mechanism capable of varying an engine compression ratio of the internal combustion engine by changing a rotational position of a control shaft upon transmission of a rotational drive force of an actuator to the control shaft through a gear reducer.
For example, Patent Documents 1 and 2 each disclose a variable compression ratio mechanism having a gear reducer designed on the differential gear principle so as to ensure not only a high reduction ratio but also a large gear module size and thereby not to cause a strength deterioration and surface wear of gear teeth due to a decrease of gear module size.
The gear reducer of the above variable compression ratio mechanism is however required to achieve a light weight, high durability and low noise/vibration characteristics, while establishing a layout within a limited vehicle space, and is still in need of further improvements.